this is not the case, the extraneous substances are examined in the ordinary
3. Determination of the Copper.-This may be carried out clectro-
lytically or volumetrically.
(a) ELECTROLYTIC DETERMINATION. 4-5 grams of the sample, as
homogeneous as possible, arc dissolved in about 200 c.c. of water with
gentle heating ; 5-6 c.c. of cone, nitric acid and 20 c.c. of dilute sulphuric
acid (10% by volume) are added and the solution electrolysed (sea article
on Copper in chapter on Metals). The conditions of working are as follows :
Winklcr electrodes ; ND100 = 0-3-0-4 ampere ; voltage, 2-2-2 volts ;
temperature, ordinary ; duration, 16-18 hours.
The weight of copper found, multiplied by 3-9283, gives the sulphate
of copper, CuS04 + 5HaO.
(6) VOLUMETRIC DETERMINATION (Zucchini's method.1). For this method
the following reagents are required :
(a) Solution containing 19-878 grams of crystallised sodium thiosulphate
per litre, and another, 8 grams of ammonium thiocyanate per litre.
(&) Iodine solution containing 5-089 grams of iodine and 20-25 grams
of potassium iodide per litre.
(c) Pure copper sulphate, solution containing 20 grams of the crystals
Solutions (a.} and (e) are of corresponding strength and 2 vols. of (6)
correspond with I vol. of (a),
In a porcelain dish are placed 60 c.c. of solution (a) and a little starch
paste 2; solution (/;) is then run in from a burette until a persistent blue
coloration appears. To another Go c.c. of («) are added, with stirring,
50 c.c. of solution (c) ( i gram of CuS()4, 5li20) and 10 c.c. of .starch
paste, this being titrated with iodine (/;) as before.
The difference («) between the volumes of (!>} used in the two cases
corresponds with i gram of CuSO,,, 5H20, and with pure, materials under
the above, conditions, this difference is very nearly 100 c.c., as it should be.
The operation is then repeated with a solution (20 grams per litre;) of
the sulphate to be tested, 50 c.c. being taken and the volume of the iodine
solution necessary measured. If w1 is the difference! in the volume, of (/;)
used in this case, the percentage of pure; crystallised copper sulphate is
(loo X n^/n.
4. Water.-5 grains of the powdered sulphate are weighed in a platinum
crucible, which is supported on a porcelain triangle inside! a larger iron
crucible ; the. latter is heateel for 15 minutes with a large. Tedu flame, the
platinum crucible being then cooled in a desiccator and weighed.
5. Iron.5-10 grams, dissolves! in 100-150 c,c. of water, are heated
for 15 minutes on a steam-bath with 5-10 c.c. of nitric acid, the iron being
then precipitated with a slight excess of ammonia and weighed as Fea03:
Fca03 X 3-475 = Ft'S04 + 7!-! A
6. Free Sulphuric Acid.io grams are dissolved to 500 c.c., the
1 Stasioni agrarie italianc, Vol. XXXII, p. 120,
a 3 grams of starch, are mixed to a panto with a little water and poured into 200 o.c.
of boiling water, the solution being boiled for a minute and allowed to cool,